I have written previously about general end of society events, this is specifically about USA.
The US has so many problems it's hard to pinpoint any particular causes of its decline. Its status in the world will almost certainly decline in this century, while its government in its current form may not even last a few decades (or possibly in a few years). There were many notable turning points which spelled out the beginning of the end, such as the creation of the Federal Reserve, Executive Order 6102, the Great Depression, the National Firearms Act, formation of the deep state, Korean war, JFK Assassination, Vietnam war, ending of Bretton Woods (gold standard), Afghanistan war, the list could go on. This decline goes far beyond the erosion of civil and natural rights, the financialization of the economy, or incompetence in governance. America is rotten to its core, it is in a spiritual decline and irreversible death spiral.
The decline has little to do with who holds political office. There is no voting your way out of sovereign debt that is unpayable, or a culture that lacks any noble values. While I do think that the Trump regime has directionally correct goals, it is unlikely he will achieve any of them. Especially firing government employees, bureaucracies metastasize like cancer and they don't shrink, they consume all available resources until the host organism is dead. America will be taxed and regulated to death, by organizations which fundamentally can't create anything but can destroy everything.
The pendulum has shifted too far towards nomos, and far away from physis. Human-made laws are never ending, arbitrary, often lack any grounding in reality, penned by bureaucrats whose job it is not to understand what it is that they're legislating. Completely dependent on cultural context, nomos can be completely dysfunctional in a dysfunctional culture. In contrast, physis represents what is natural, chaotic, the inherent order of things or the way things are meant to be. Natural law is rooted in morality, which must have a spiritual basis, in contrast to manmade law which is rooted in tradition and culture. Without physis, the rule of nomos leads to things like squirrels being executed by the state.
Spiritual death
There is a great spiritual decline in the USA, which may be correlated with decreasing participation in organized religion. A secular society is not irreligious, it has replaced traditional religion with secular religion: in the USA, capital may as well be God. There's a reason why other countries call America "Great Satan", and it isn't about our freedoms (in fact, USA is a lot less free than places around the world with small government). No surprise that billionaires see themselves as descendants of the ancient pharoahs, above nationality and laws, destined to inherit the Earth. The deification of capital and its consequences have been a disaster for the human race.
Perhaps one of the worst consequences of the death of God is secular morality. One has to ask why is theft wrong, because it deprives another person of their belongings. Or why murder is wrong because it deprives another person of life. But to a bureaucrat, why are these considered morally evil at all, or why should we care? As we stray further from physis, or natural law, the laws, rules and regulations lack a natural basis or ethical grounds. Exceptions can easily be carved out, such as theft in the form of taxation, murder in warfare or law enforcement immunity, adultery in no-fault divorces, absolute lies in media/propaganda (same thing), and so on. The USA in its current form is an exceptionally litigious country, rife with frivolous lawsuits, patent trolls, political lawfare, but it is also a morally bankrupt country.
The left has historically championed social justice, but they are unaware of the irony of demanding that the state carry out justice. Equality demands that both the robber and the robbed to be punished, compromises between the thinker and the fool by meeting half-way. In redistributive justice, the state is the winner in any conflict, there is no incentive for them to be concerned with morality or truth. Leftists demand rights from the very entity which has the power to deny people their natural rights, and they are also the biggest advocate for stripping rights away via arbitrary rules and regulations, such as censorship, gun control, environmental regulations, discrimination of race, gender, etc. In principle, discrimination based on prejudices are all morally harmful. But to take a litigious approach in an attempt to reduce harm caused by discrimination may have the unintended effect of amplifying it. The civil rights movement of the 1960s championed legal rights for people of color, but had little effect on reducing racial animosity. Americans are as distrustful as ever of ethnic out-groups, it has turned parts of America into diverse, low-trust cities, while others remained homogenous, high-trust communities.
I am not a Deist or follower of the Abrahamic religions, actually I am agnostic and a lay Buddhist. I'm not prescribing Christianity as the solution to society's spiritual and moral decay, but it is a solution.
Low culture
Critics say that America lacks culture, which isn't true: it just has low culture. A culture that caters to the common man, the lowest common denominator, perhaps even an anti-intellectual culture about as repressive as Maoist era cultural revolution. If one learns value from society, one will inevitably get dragged in to various failure modes like smoking weed all day, food delivery by private chaffeurs if one is privileged, overspending on multiple credit cards, cancelling others based on their political views, unhealthy obsession over sportsball, etc. It is a low culture that is removed from spiritual underpinnings, more of a free-for-all arena where there is tolerance of increasingly depraved behaviors.
American elites used to mimic the high culture of Europe, be educated and have a sense of responsibility or noblesse oblige. In a sense, one had to earn the right to rule, and that is no longer the case. We have a state that rules with or without consent, they have no legal boundaries anymore and consider themselves as rulers. This top-down fascistic megalomania trickles down to those with even a modicum of power, as police brutality, low-level government corruption, HR-ification of workplaces which is just a convenient way for the state to intrude in daily life as a wageslave.
Perhaps one of the most disturbing developments is the ambient financialization of every social interaction. Social media, professional networking, informal payment platforms, centralized crypto exchanges, "sharing economy" apps, are all races to the bottom of trying to profit by being middlemen between what used to be cash, barter, or quid pro quo exchanges. As institutions try to own everything, eventually people will own nothing (and be happy). The complete normalization of pervasive institutions in all aspects of life is the path to totalitarianism, the only question is whether that will be more like Brave New World or 1984, probably the worst of both.
American culture lacks an élan vital, other than just hoarding useless fiat currency. So many bugmen humble-bragging on Blind about their impressive net worth, but self-deprecating with their lack of friends and community or worthwhile relationships. These are the very people who are idolized for their material wealth, yet they live vacuous, meaningless lives. The poster boy for this may be Patrick Shyu (TechLead), who may have recently just realized the error of his ways (as a millionaire). The Silicon Valley / Wall Street hedge fund rat race has no worthwhile endgame, other than a stack of cash at the end, which is worthless on a deathbed.
There is no more America which accomplishes anything worthwhile to advance humanity, only institutions which redistribute wealth from many to the elite. The elite themselves have no higher ideals, and are often incompetent grifters, the system rewards political ass-kissing and is how people as unqualified as Kamala Harris almost usurped the highest elected office. Nobody elected her and there were much better options even within her own party. These days, it's all about what your country can redistribute for you rather than what you can contribute, an inversion of JFK's inaugural address.